Electrical connectors are devices providing for connection between conducting objects, and a number of devices of various configurations and sizes for this purpose were offered in the art. One type of electrical connector is designed specifically for the mounting on printed circuit board by soldering. Such connectors usually consist of a plug (male) connector and a receptacle (female) connector, and they interconnect associated circuits of two parallel printed circuit boards. With a general trend toward reduction of electronic devices in size, the space between printed circuit boards is being reduced at a fast pace, and in many cases it can be as little as a few millimeters.
Example of connectors for printed circuit boards can be found in U.S. Pat. No. 5,224,866; Japanese Utility Model Disclosure Hei 3 (1991)-126389 and Japanese Patent Disclosure Hei 4 (1992)-43579. Such conventional connectors for printed circuit boards have a number of flat contacts intended for the connection by means of surface mounting technology (SMT) to contact pads of two parallel printed circuit boards. Contacts of a connector mounted on one of the printed circuit boards are designed so that they have relatively long effective length in order to be able to provide sufficient contact pressure (normal force) developed by the spring-loaded design of the contacts against contacts of the mating connector. Such an arrangement makes it possible to implement connectors for printed circuit boards having a high density of contacts (up to 0.5 mm pitch).
However, elasticity of the contacts made by stamping from a resilient metal sheet is rather limited. It is especially difficult to achieve sufficient elasticity of contacts in portable communications devices such as personal handy phones (PHS) in which the gap between boards can be as little as a few millimeters while the component density is very high. In addition, in the event of misalignment between two printed circuit boards, when the connectors themselves are not exactly aligned with each other, an attempt to forcibly join connectors can result in damage of deformation of the connectors or their contacts.
A method to handle misalignment between two boards is offered in U.S. Pat. No. 5,501,663 or in Japanese Patent Disclosure No. Hei 4 (1992)-370677. This method consists in making at least one housing of two sections allowing for certain flexibility due to contacts made in a zigzag configuration, thus increasing their effective length. However, in order to achieve the flexibility, it is necessary to increase physical dimensions of the connector, thus diminishing its suitability for small-size high-density applications.
Another problem observed in high-density electrical connectors is related to the edges of the contacts that are fabricated, as mentioned above, by stamping from resilient metal sheet material and that become contacting surfaces with the mating contacts. The point is that the smoothness of the edge surfaces obtained by shearing is inferior to the face surface produced by rolling, thus making it difficult to obtain stable and reliable electrical connections.
In order to solve the problem related to poor quality of the contacting surfaces, it was offered to cut contacts from a very thin metal sheet, bend them to a U-shaped configuration and place them over and around posts of the insulating housing so that the rolled surface becomes the contacting surface (Japanese Patent Disclosure Hei 3 (1991)-45873). Another proposed solution concerned contacts consisting of two arms originating from a flat base that are twisted 90.degree., thus providing a relatively wide surface of contact (for example, see Japanese Patent Disclosure Hei 3 (1991) -70350).
However, solutions in which such contacts with rolled surfaces as the contacting surfaces are used can be offered only for relatively large connectors with a low or medium density of contacts (with a pitch over 1 mm), and can not be applied to small-size high-density connectors.